Isoflurane or 1-chloro-2,2,2,-trifluoroethyl difluoromethyl ether is an inhalation anesthetic. See U.S. Pat. Nos. 3,535,388 and 3,535,425. Although the metabolic pathways of isoflurane are not well defined, it is known that the compound is metabolized in the body to release inorganic halides into the blood. See Greenstein, et al. Anesthesiology 42, 420-424 (1975) and Mazze, et al. J. Pharmacal. Exptl Therap. 190, 523-529 (1974). Clinical studies in both laboratory animals and man indicate that the presence of inorganic fluoride in the blood caused by the metabolism of anesthetics containing fluorine is related to renal failure. Therefore, it is desirable to retard the metabolism of an anesthetic containing fluorine, such as isoflurane, to minimize the release of inorganic fluoride into the blood.